[autotest] Check for 'image_name' in autoupdate control file

I intended to check to see if a variable called 'image_name' was defined
in the autoupdate control file and switch some behavior based on that check.
Instead, I was checking to see if a variable named after the _contents_ of
the variable image_name was defined in the control file.  Whoops.

BUG=None
TEST=./server/autoserv test_suites/dev_harness and then look for a wget
     command in the test log that mentions autotest/packages
TEST=./run_remote_tests.sh --board=x86-generic --ssh_port=9222 --remote=127.0.0.1 --use_emerged suite_Smoke

Change-Id: I5c034b4d1c54ed273eae62cc3549481d573a0a0e
Reviewed-on: https://gerrit.chromium.org/gerrit/15777
Tested-by: Chris Masone <cmasone@chromium.org>
Commit-Ready: Chris Masone <cmasone@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index b3d168d..9b20d65 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -136,4 +136,4 @@
 # the above value for dev_server when this config is parsed, but leave the
 # name field to be populated later.  Sadly, that doesn't parse.
 image_url_pattern: %(dev_server)s/update/%%s
-package_url_pattern: %(dev_server)s/static/%%s/autotest/packages
+package_url_pattern: %(dev_server)s/static/archive/%%s/autotest/packages